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Polymorphic relationship in Rails refers to a type of Active Record association. This concept is used to attach a model to another model that can be of a different type by only having to define one association.
They essentially do the same thing, the only difference is what side of the relationship you are on. If a User has a Profile , then in the User class you'd have has_one :profile and in the Profile class you'd have belongs_to :user . To determine who "has" the other object, look at where the foreign key is.
In Ruby on Rails, a polymorphic association is an Active Record association that can connect a model to multiple other models. For example, we can use a single association to connect the Review model with the Event and Restaurant models, allowing us to connect a review with either an event or a restaurant.
There is a known issue with Rails 3.1.1 that breaks this functionality. If you are having this problem first try upgrading, it's been fixed in 3.1.2
You're so close. The problem is you're misusing the :source option. :source should points to the polymorphic belongs_to relationship. Then all you need to do is specify :source_type for the relationship you're trying to define.
This fix to the Widget model should allow you do exactly what you're looking for.
class Widget < ActiveRecord::Base
has_many :widget_groupings
has_many :people, :through => :widget_groupings, :source => :grouper, :source_type => 'Person'
has_many :aliens, :through => :widget_groupings, :source => :grouper, :source_type => 'Alien'
end
As mentioned above, this doesn't work with rails 3.1.1 due to a bug on :source, but it's fixed in Rails 3.1.2
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